In the art of upward acting doors, torsion spring actuated counterbalance systems are widely used for counterbalancing the weight of the door. In rollup type or so-called sheet doors, in particular, the counterbalance mechanism is relatively uncomplicated, of necessity, to minimize the cost of fabrication and installation, since such doors are typically used in large numbers in low cost installations, such as so-called miniwarehouses. A typical rollup type door for miniwarehouse applications includes a flexible sheet closure member which is wound on a series of spaced apart drums which are supported on a rotatable shaft. The shaft is mounted on spaced apart brackets secured to a vertical wall in which the door opening is formed. At least one torsion type counterbalance spring is sleeved over and connected at one end to the door drum shaft and the opposite end of the spring is operably connected to one of the stationary wall brackets.
The adjustment of torsion type door counterbalance springs is a relatively difficult exercise and several attempts have been made to develop a simplified mechanism for adjusting and locking the torsion spring at the end which is operably fixed to the door support structure, including the so-called header bracket or wall bracket. However, in a continuing effort to improve adjustment or tensioner mechanisms for adjusting torsion springs for rollup type doors, the present invention has been developed.